Serum concentrations of bioactive luteinizing hormone (LH) and of testosterone were measured in adult male rhesus macaques at the time of, and at least 6 wk after orchidectomy. The effects of anesthesia alone and of sham surgery on the secretion of these hormones were also studied. Contrary to expectations based on current notions of the negative feedback actions of testosterone on gonadotropin secretion, pulsatile LH release was absent for an average of 9.3 h immediately after removal of the testes. Animals that were subjected to sham surgery or anesthesia alone showed a delay of 4.4 h in the reappearance of LH secretion, similar to the lull in LH pulsations normally observed at the time of day. When LH secretion resumed in the acutely castrated animals, the pulses continued for the remainder of the sampling period and did not show the midmorning decrease in activity characteristic of intact or sham-operated animals. In the animals that were castrated, circulating cortisol was elevated approximately twofold above levels observed in sham-operated animals for a period of 8 h, beginning immediately after castration. In the long-term (greater than 6 wk) castrated male macaques, circulating bioactive LH levels were eightfold greater (24 micrograms/ml) than levels observed in intact animals (3 micrograms/ml). The frequency of LH pulses in the castrated animals, as determined by PULSAR analysis, was significantly influenced by sampling frequency. When blood samples were taken at 15-min intervals for 24 h, LH pulse frequency averaged 7 pulses/12 h. If samples were collected every 7 min for 12 h, the frequency increased to 13 pulses/12 h.(ABSTRACT TRUNCATED AT 250 WORDS)